Satellite communication systems have used phased array antennas to communicate with multiple users through multiple antenna beams. Typically, efficient bandwidth modulation techniques are combined with multiple access techniques, and frequency separation methods are employed to increase the number of users. Because electronic environments are becoming increasingly dense, more sophistication is required for wireless communication systems. For example, with all users competing for a limited frequency spectrum, the mitigation of interference among various systems is a key to the allocation of the spectrum to the various systems.
Digital Beam Forming (DBF) systems have been developed for use in communications systems and radar systems. DBF systems require accurate direction of arrival (DOA) information to efficiently position beams and nulls in their antenna radiation/reception patterns. In DBF systems in which transmitters and receivers move relative to each other, DOA information is continually updated to maintain accuracy. Using accurate and up-to-date DOA information, a DBF system can improve its allocation of resources by placing beams on active and high-traffic areas, while avoiding unnecessary coverage of large inactive regions. This is particularly important when satellites are being used because the efficient determination of directions of arrival can decrease the required processing load and decrease the amount of on-board power required.
There is a need for a method and apparatus to accurately and efficiently determine a DOA estimation of incident signals received by phased array antennas in DBF systems. There is also a need for a method and apparatus to accurately and efficiently determine a DOA estimation of signals transmitted by phased array antennas in DBF systems. In addition, these needs are especially significant for satellite communication systems that include non-geostationary satellites and/or geostationary satellites.